The invention relates to filter centrifuge with a drying device for the moist solids collected within the centrifuge drum wherein the centrifuge has a solids outlet opening that opens into a solids outlet housing.
For drying the moist solids collected in the centrifuge drum different drying processes are conventionally used.
In diccontinuous filter centrifuges, e.g., as disclosed In German Patent Application 33 40 636, the filter cake in the centrifuge is freed to the greatest possible extent from the mother liquor and is optionally washed with liquid media, is then mechanically demoisterized by centrifugal forces and subsequently removed from the centrifuge drum. The moist solids thus obtained are moved into a solids outlets housing connected downstream of the centrifuge drum and are then conveyed into a thermal drying device, as disclosed in German Patent Application 31 41 549.
The disadvantages of such a process and device are as follows:
a) high apparatus expenditure due to the combination of a plurality of components (centrifuge, buffer container, transporting device, thermal dryer ), and considerable expenditure for process automation; PA1 b) great space requirement at different heights; PA1 c) increased risk of failure in the case of negative product properties of the solids, such as baking on the walls, conglutination etc; as well as a plurality of transfer or interface locations for process automation; PA1 d) increased service and maintenance expenditure as well as replacement part storage; PA1 e) increased cleaning expenditure when starting up the device. PA1 a) long filtration and drying times, thus reduced product capacity and uneconomical efficiency; PA1 b) increased risk of filter cake compaction; PA1 c) long occupation periods of the device components arranged upstream and downstream, capacity loss of the entire production facility; PA1 d) limited economical use when the centrifuge cycle time in relation to the drying time is approximately 1:1; PA1 e) high gas throughput results in relatively high energy costs for heating the drying gas; PA1 f) relatively high operating cost for the recycling of the outflowing gas in a gas recirculating device; PA1 g) high additional expenditures for compressors, heat exchangers, gas recirculating device. PA1 a) susceptible to imbalance problems for products that can be easily filtered and have a high density and for spontaneously filtrating solids; PA1 b) problems in regard to non-uniform filtration and washing steps; PA1 c) acceleration values for the centrifuging step with 600-700 G is lower than for filter centrifuges; this results in extended cycle times with reduced mechanical moisture removal; this also results in longer total cycle times and increased energy costs due to the higher initial moisture before drying and the relatively long drying times; PA1 d) metallic filter fabrics are problematic in comparison to textile fabrics with respect to cleaning when conglutination of solids occurs ; in the case of breakdown, the accessibility of the machine with regard to inspection and cleaning is cumbersome; PA1 e) the use of centrifuge dryers in multiproduction facilities, especially in the pharmaceutical industry, results in relatively long downtimes when a product changeover needs to be made; PA1 f) the centrifuge dryer has no solids outlet housing and the product removal is carried out pneumatically pulsating fashion via an annular channel in the outward direction. Thus, the removal of the moist product is not possible. In the case of breakdown a very high time and labor expenditure is thus to be expected. PA1 a centrifuge drum having a solids removal opening for solids collected in the centrifuge drum; PA1 a solids drying housing into which the solids removal opening opens; PA1 the solids drying housing having a sieve bottom, a gas inlet for introducing a drying gas, and a gas outlet for removing the drying gas. PA1 a) compact system, all method steps from the processing of the suspension to the dried end product can be realized within one device; PA1 b) all discontinuous filter centrifuges can be correspondingly retrofitted; PA1 c) optimal capacity use by performing separately and parallel of the method steps of centrifugation and drying; PA1 d) in regard to process control, the system requires only one control unit; PA1 e) greater application range because the filter cake removal can be performed in the moist state of the solids as well as in a pre-dried state, respectively, in the finally dried state; PA1 f) the device, in general, is not subject to pressurized container regulations; PA1 g) reduced operating costs due to the more effective pre-moisture removal of moisture by increased centrifugal forces, reduced amount of drying energy; PA1 h) higher operative safety; no imbalance problems; due the use of textile filter fabrics, reduced danger of conglutination or plugging.
In diccontinuous filter centrifuges, as disclosed in German Patent Application 44 17 310, having a pressure-tight encapsulated drum interior, subsequent to the mechanical demoisterization a convective solid bed drying with pressurized gas and flow of gas through the filter cake from the interior to the exterior can be performed. This process is only suitable for crystalline solids that can be easily filtered. A prerequisite is a specific high gas throughput. This system has the following disadvantages:
In centrifuge drying devices known from U.S. Pat. No. 5,163,895 the mechanical demoisterizing step is followed by convective drying in a pressure-tight closed drum, depending on the material to be dried. After the segment-wise removal of the filter cake from the drum the interior of the drum can be used for a fluidized bed drying process which can be enhanced by applying a vacuum.
In centrifuge dryers the drum is embodied as a drying container and provides multiple options with respect to drying processes. In such drums only metallic filter media can be used. The system has the following disadvantages:
It is therefore an object of the present invention to provide a discontinuous filter centrifuge with which the known disadvantages of the system can be prevented whereby it is especially desired to achieve an optimal method-technological drying of the moist solids collected in the centrifuge drum and still with minimal mechanical expenditure and minimal space requirement without adversely affecting the centrifuge capacity.